Pulsation-preventing apparatus for centrifugal compressors.



, S. A. MOSS. I PULSATION PREVENTING APPARATUS FOR CENTRIFUGALCOMPRESSORS.

APPLICATION FILED FEB. 2. I911. 1,280,81 1. Patented Oct. 8, 1918.

I 2 SHEETS-SHEET 1.

- Inventor; Sal-ford .24. M 035,

Patented Oct. 8,1918.

2 SHEEISSHEE[ 2.

Inventor;

SanFor-d 0 Moss, b5

s. A. MOSS. 'PULSATION PREVENTING APPARATUS FOR CENTRIFUGAL COMPRESSORS.

APPLlCATlON FILED FEB. 21 I917.

' UNITED snares reaper enema.

SANFORD A. MOSS, 0F LYNN, MASSACHUSETTS, ASSIGNOR T0 ELECTRIC, COMPANY,A CORPORATION OF NEW YORK.

PULSA'IION-PREVENTING APPARATUS FOR CENTRIFUGAL COMPRESSORS.

Specification of Letters Patent.

Patented Oct. 8, 1918.

Application filed February 2, 1917. Serial No. 146,127.

pressing air, or other gases, and has for its object generally toprovide an improved apparatus for preventing pulsations of the air orother gas flowing through the ma chine.

In the following specification the compressor is described as a machinehandling air, but it will be understood that my invention is not limitedto this use.

Pulsations are found to occur under certain conditions of light load andare now known to depend on the volume of air which the machine ishandling and on the pressure at which it is being delivered. In otherwords, for every volume there is a critical pressure above'whichpulsations are liable.

to occur; and vice versa for every pressure thereis a critical volumebelow which pulsations are liable to occur. The critical pressures andvolumes in difi'erent machines vary considerably, however, and for anyparticular machine they can only be determined by experiment.

As already stated, the point at which pulsations occur depends on thevolume and the pressure, which in turn are proportional to the speed ofthe machine, and the ratio of volume to speed, or approximately ratio ofvolume to square root of the pressure is known as the load coeflicientof a compressor. If this coefficient is relatively large, the machinewill operate smoothly; but if it decreases below a certain value thenpulsations will occur. There is thus for every compressor a criticalvalve of the load coeflicient below which pulsations will occur. Thisvaries for different machines and can onlybe determined by experiment.

It is well known that pulsations in a compressor may be prevented, atleast to a great extent, by throttling the flow of air through it, as bythrottling the intake, or by wasting air from the delivery side of themachine, or by by-passing it from the delivery side to theiintake. Ininstallations where it is de sirable that the machine be operated atloads where pulsations are liable to occur such valves are usuallyprovided. Such valves may be termed generically pulsation preventingvalves, and they have been actuated manually and by various automaticarrangements.

It is also now known, as set forth in the application of Christopher A.Schellens, Serial No. 146,112, filed of even date herewith, that inorder to prevent pulsations the pulsation preventing valve should beactuated in accordance with the value of the volume divided by thesquare root of the pressure, 2'. e., in accordance with the loadcoefiicient of the machine. If so actuated such valve would be actuatedby justthe right amount and under the proper conditions to prevent pulsations occurring. As will be appreciated, the operation of thepulsation preventing valve, as the throttling of a valve in the intake,or the opening of a by-pass valve, or both, is desirable only whennecessary as it means, of course, a loss of energy.

More specifically the object of my invention is to provide an improvedarrangement which is applicable under varying conditions to prevent theoccurrence of pulsations.

For a consideration of what I believe to be novel and my invention,attention is directed to the accompanying specification and the claimsappended thereto.

In the accompanying drawings, Figure 1 is a vertical sectional view of apulsation preventing apparatus embodying my invention; Fig. 2 shows theapparatus of Fig. 1 applied to a centrifugal compressor; Fig. 3illustrates a modified form of my invention wherein the same is appliedto a compressor operating under a condition diflerent from that shown inFigs. '1 and 2, and Fig. 4 shows another form of my invention.

' Referring tothe drawings, Figs. 1 and 2, 5 indicates a centrifugalcompressor having an inlet conduit 6 and a discharge conduit 7. It

may be driven by any suitable form of prime mover, as for example, asteam turbine. The inlet conduit 6 comprises an enlarged section formedof two conical-shaped members 8 and 9 and a straight section 10 whichconnects the conical member 9 to an elbow 11 leading to the eye of theimpeller. Located in the enlarged section is a float 12 which rides onthe incoming air and, as is 10 explained more fully hereinafter, tendsto assume a position which varies with the volume entering thecompressor. The float 12 is guided by a stem 13 which slides in a guidesleeve 14 and it is connected by a link 15 to 15 a plate 16 carried by abutterfly valve 17 which is located in the pipe section 10. The link 15is preferably arranged so that its length may be adjusted, and to thisend it is shown as being provided intermediate be- 20 tweenits ends witha turn buckle 18. The butterfly valve 17 is adapted to throttle theintake of the compressor to prevent the occurrence of pulsations. Theplate 16 is provided with a series of openings 19, into any one of whichthe end of link 15 may be connected. By this arrangement the float 12,while having one movement, may be set so that it tends to impart adesired characteristic movement to the valve 17 20 indicates so thespindle of the valve journaled in the wall of pipe section 10. On anextension of one end of the spindle 20 isfixed a rod 21 carrying anadjustable weight 22 which tends to bias the butterfly valve to openpos5 sition, and an arm 23 having a series of 'openings 24 in its end.Connected into one of the openings 24 is one end of a link 25, the otherend of which is adjustably connected to a stem 26 carried by the movablean element of a pressure responsive device.

In the present instance this pressure responsive device is shown ascomprising a cylinder 27 within which moves a piston 28, to which stem26 is connected such piston forming a as movable abutment. Connectedwith cylinder 27 below piston 28 is a pipe 29 which leads to thedischarge side of the compressor. The movable abutment 28 is thussubjected to the pressure on the delivery side of the an compressor.

With the arrangement as just described it will be seen that thebutterfly valve 17 is subjected to two positioning forces; oneproportional to the volume and represented by '55 the force exerted bythe float 12, and the ;other proportional to the delivery pressure andrepresented by the force exerted by the movable abutment 28. These twoforces act on opposite sides of the spindle 20 and are to thus opposedto each other.

As stated above, it is now known that in order to prevent pulsations thepulsation preventing .valve'should be actuated in accordance with thevolume divided by the as square root of the pressure. Now forcentrifugal machinery at a given load coefficient, the pressure varieswith the square of the speed, so that the value of volume squareddivided by pressure is given by the volume divided by the square root ofpressure; 2'. 0., the load coeflicient. In fact one is the square of theother.

In the operation of my apparatus the float 12 is connected to thebutterfly valve 17 at such an obliquity of the link 15 and the floatforce so varies with the volume that the float exerts an opening forceupon the butterfly valve spindle which is proportional to the square ofthe volume, and the movable abutment 28 is connected to the valve 17through the arm 23 so that it exerts a closing force proportional to thedelivery pressure. The resultant force acting on the valve 1'? is thusproportional to the volume squared divided by pressure, which in turn isproportional to the load coeflicient. The arrangement is such that forall values of the load coefficient above the critical value the valve iswide open. When the critical value of the load coefficient is 9 reachedthen the apparatus will operate the butterfly valve to throttle theinlet by a suflicient amount to maintain the load coefiicient at, orjust slightly above, the critical value. As already pointed out, thecriti- 5 cal load coefficient value is determined experimentally foreach machine. The arrangement may be termed a universal automaticpulsation preventing apparatus, as it automatically takes account ofboth the volume and the pressure in the actuation of the pulsationpreventing valve.

T have found by experiments that throttling the intake of a compressorwill prevent pulsations down to a certain low flow, after which furtherthrottling will not prevent them. The only means of which I am now awarefor then preventing pulsation is by wasting air from the delivery sideof the compressor or by by-passing it from the delivery to the suctionside thereof, the latter arrangement being generally preferable. InFigs. 3 and a l have shown arrangements for preventing pulsationswherein a throttle valve in the intake is first 'operated and after itbecomes ineflective to prevent pulsations then a waste or by-pass valveis opened to waste air from the delivery side of the compressor orby-pass it therefrom to the suction side of it. 7

Referring now to Fig. 3, 30 indicates a centrifugal compressor having aninlet conduit 31 and a discharge conduit 32'. It is shown as beingdriven by a steam turbine, a portion of which is indicated at 33. 34cindicates the valve mechanism which controls the admission of elasticfluid to the turbine, and 35 a fluid actuated motor for operating it.The turbine driven compressor set is provided With a usual form ofconstant vol- 130 aeeden ume governor comprising a pivoted beam 36connected at one end by a rod 37 to a float 38 in the inlet conduit 31.The other end of beam 36 is connected through links 39 and 40 to thefluid motor 35. 41 indicates the constant volume governor weight and 42the hand wheel for adjustin it along the scale on the beam. The fluimotor 35 is also suitably connected to the speed governor 43 as shown.The operation of a constant volume governing mechanism, as justdescribed, is well known. The weight 41 is set on the scale for thedesired volume of flow and the fioat 38 acts on the beam to tilt it soas to cause the fluid motor 35 to open and close the valve mechanism 34to maintain theturbine 33 at the speed required to supply the volume ofair desired. If the volume of. air flowing tends to decrease, then thefloat 38 lowers a little, thus causing the beam 36 to tilt and open thevalve mechanism 34 so as to admit more elastic fluid to the turbine andincrease the speed, and thus cause the compressor to take more air. Onthe other hand, if the volume tends to increase then the opposite actiontakes place. The speed governor 43 is normally inactive, the turbinebeing wholly underthe control of the constant volume governor, and onlycomes into play to take control in case of excess speed. It is some whatof the nature of an emergency governor.

45 indicates a butterfly valve in the inlet conduit, and 46 an operatingarm for it. The free end of arm 46 is connected by a rod 47 to an arm 48of a bell crank lever, which lever is pivoted on a frame 49. Sliding inguides on the frame 49 is a-cam plate 50 provided with cam slots 51 and52 each comprising an angular portion and a straight portion. The otherarm 53 of the bell crank lever has a pin or roller 54 at is end whichprojects into the slot 51. 55 indicates a pipe for wasting air from thedischarge side of the compressor. It is shown as connecting thedischarge side of the compressor to the inlet in advance of the constantvolume governor float 38, this being the preferred arrangement. In thepipe 55 is a butterfly valve 56 having an operating arm 57 con-' nectedby a rod 58 to one arm 59 of a bell crank lever pivoted on the frame 49.The other arm 60 of the bell crank lever has a pin or roller 61 at itsend which projects into the cam slot 52. The cam plate 50 is connectedby a link 62 to one arm 63 of a threearm lever, which lever is pivotedat 64. A second arm 65 of the three-arm lever is connected to the end ofastem 66 carried by a piston 67 which moves in a cylinder 68. The end ofcylinder 68 is connected by a pipe 69 to the discharge side of thecompressor. The piston 67, which forms a movable abutment, is thussubjected to the pressure on the delivery side of the compressor. Thethird In operation the constant volume governor weight 41 is set for thedesired volume of flow and the weight 71 is adjusted on the arm 70 to aposition on the scale corresponding to this flow. The valve 45 in theinlet conduit 31 will be wide open and the valve 56 in conduit 55closed. If new the load c0- eflicient reaches a'value at-whichpulsations are likely to occur, then the increased delivery pressureacting on the piston 67 will lower it, thereby turning the three-armlever in an anti-clockwise direction. This will move the cam plate 50toward the left and the pin or roller 54 on the end of bell crank leverarm 53 will ride up the inclined portion of cam slot 51 thus-tilting'the bell crank lever so that the end of lever arm 48 moves toward theleft and closes to a greater or less extent the butterfly valve 45. Thisaction may continue until a condition is reached when further throttlingof valve 45 will not preventpulsation. The pin or; roller 54 then Vpasses into'thstraight portion of cam slot 51 and throttle valve 45 isthen upon further movement of cam plate 50 held stationary. During themovement of cam plate 50 and while the Olpin or roller 54 Was moving upthe incline portion of cam slot 51, the pin or roller 61 was moving alonthe straight portion of cam slot 52, the va ve 56 remaining closed. Ator about the time the pin or roller 54 reached the straight portion ofcam. slot 51, the pin or roller 61 reached the angular portion of camslot 52, and when it starts to ride up this angular portion, the bellcrank lever of which it formsa part is turned on its pivot to open theby-pass valve 56. This permits air to be wasted from the delivery sideof the compressor and prevents the occurrence of pulsations. By thisarrangement, it will be seen that the pulsation preventing valves 45.

Figs. 1 and 2. In fact, it is the arrangement of Figs. 1 and 2 a lied tothe valve mechanism of Fig. 3. ince the arrange-, ment of the valvemechanism of Fig. 3 is the same as that of Fig. 2 I have applied the.same reference numerals to corresponding parts. The arrangement of Fig.4 difi'ers from that of Fig. 3 in that the arm of the three-arm leverinstead of carrying a weight 71 has its free end connected by a link 7 5to one arm of a lever 76. The other arm of the lever is connected by arod 77 to a float 7 8 located in the intake conduit 81 the same as isthe constant volume governor float 38, Fig. 3, and the float 12 ofFig. 1. The operation of the'arrangement of Fig. 4c is the same as thatof Figs. 1 and 2, the float 78 and pressure responsive device 67 bothacting upon the pulsation preventing valve mechanism and in oppositedirections. In the present instance, however, the pulsation preventingvalve mechanism comprises the two valves 45 and 56, the one in the inlet31 and the other in the by-pass 55, the two be.- ing operated insequence. In view of the 6X- planations already given of the operationof the arrangements of Figs. 1, 2 and 3, the operation of that of Fig.at will be readily understood without further description.

In accordance with the provisions of the patent statutes, l havedescribed the principle of operation of my invention, together with theapparatus which I now consider to represent the best embodiment thereof;but I desire to have it understood that the apparatus shown is onlyillustrative and that the invention can be carried out by other means.

What I claim as new and desire to secure by Letters Patent of the UnitedStates, is

1. The combination with a centrifugal compressor having a pulsationpreventing valve mechanism comprising a valve member, of means forautomatically regulating said valve member comprising a float in theinlet vof the compressor, a movable abutment responsive to the'dischargepressure of the compressor, and means connecting the float and theabutment to said valve member so that said float acts in a direction toopen the valve member and said movable abutment acts in a'direction toclose it.

2. The combination with a centrifugal compressor having a pulsationpreventing valve mechanism comprising a valve member and a pivotedspindle, of means for automatically regulating it, comprising a float inthe inlet of the compressor, a movable abutment responsive to thedischarge pressure of the compressor, and means connecting the float andthe abutment to said spindle so that saidfloat acts in a direction toopen the valve member and said movable abutment acts in. a direction toclose it.

3. The combination with a centrifugal compressor having a pulsationpreventing valve mechanism comprising a valve member, of means forautomatically regulating said valve member comprising a three-arm lever,means connecting'one arm of said lever to the valve member, a float inthe inlet of the compressor, a movable abutment subjected to thepressure on the delivery side naeaeri ber, of means for automaticallyregulatingsaid valve member comprising a float 1n the inlet of thecompressor, a movable abutment responsive to the discharge pressure ofthe compressor, and means connecting the float and the abutment to saidvalve member in such manner that they act on the valve member inopposition to each other.

5. The combination with a centrifugal compressor having a by-passconduit connected with the discharge end thereof, of a throttle valve inthe inlet, a throttle valve in the by-pass conduit, a float in theinlet,a movable abutment subjected to the pressure on the delivery side of thecompressor, and means connecting said float and abutment to the twovalve mechanisms.

6. The combination with a centrifugal compressor having a by-passconduit connected with the discharge end thereof, of a throttle valve inthe inlet, a throttle valve in the by-pass conduit, a float in theinlet, a movable abutment subjected to the pressure on the delivery sideof the compressor, and means connecting said float and abutment t0 thetwo valve mechanisms and operating to actuate them successively.

7. The combination with a centrifugal compressor having a by-passconduit connected with the discharge end. thereof, of a valve in theinlet, a valve in the by-passconduit, a three-arm lever, meansconnecting one of said arms to the valves to operate them successively,a movable abutment subjected to the pressure on the delivery side of thecompressor, means connecting said abutment to another of said arms, andmeans for subjecting said third arm to a force proportional to thevolumepassing through the compressor.

8. The combination with a centrifugal compressor having a by-passconduit connected with the discharge end thereof, of a valve in theinlet, a valve in the bypass conone of said arms to the valves tooperate them successively, said means comprising a plate having camslots therein, a movable abutment subjected to the pressure on thedelivery side of the compressor, means connecting said abutment toanother of said arms, and means for subjecting said third arm to a forceproportional to the volume passing through the compressor, the forces onthe three-arm lever due to said abutment and said last named meansacting in opposition to each other.

9. The combination with a centrifugal compressor having a by-passconduit con- .duit, a three-arm lever, means connecting nected with thedischarge end thereof, ofa 'ment to another of said arms, a float in thevalve in the inlet, a valve in the by-pass inlet of the compressor, andmeans connectconduit, a three-arm lever, means connecting ing said floatto the third arm of said three- 10 one of said arms to the valves tooperate arm lever.

them successively, a movable abutment sub- In Witness whereof, I havehereunto set jected to the pressure on the delivery side of my hand this19 day of January 1917.

the compressor, means connecting said abut- SANFORD A. MOSS.

